If one opens a standard MIDI file in QuickTime Player, chooses "Get Movie Properties" from the Movie menu, and selects "Music Track" and "Instruments" from the popup menus, the resulting instrument selection window will let you open an on-screen MIDI keyboard. Just double-click any instrument, and you'll see something like the image at left.

As this dialog does not allow you to record or alter the sequence contained in the MIDI file, it is not particularly useful from a composition standpoint. However, it does give you a chance to easily try out all the different timbres built into the Quicktime MIDI module. There are far more sounds available than you might expect, and several of the built-in timbres are provided under license from Roland USA.

Or I've been using MidiKeys, which works and appears to offer more keys (the "QWE..." row is a lower octave, with "123..." black keys, and the "ZXC..." row is a higher octave, with "ASD..." black keys).

Agreed. This is old news and barely a tip. If you wanted to make it a good tip, you might mention that you can change from QuickTime instruments to SoundFont and DLS sound banks (based on what's chosen in the Sys Prefs/QuickTime conrol panel). You might also mention that the keyboard responds differently when you hold modifier keys: e.g. press control and play a note on the keyboard.... then move the mouse = pitch bend. Press Command and click to play a note to play it louder....

Does anyone know why nothing happens when I double click on the instruments listed? I'm running Panther, and have tried opening a bunch of my midis. I can clearly see the list of different instruments, but when I double-click them,...nada.

With the QuickTime keyboard you can use the command and shift keys while clicking the keyboard to amplify the volume. Both together is loudest. The control key allows you to bend the pitch of the current note.

I'm so tired of these hints that don't work. Doesn't work for me either - although I am using latest versions. Maybe the person giving a hint like this should mention if he is using older versions or a special setup...

Sorry I didn't catch this when I posted the hint, but my main Mac has QTPro on it, and I didn't even think about it. But I just tested with a non-Pro machine, and the hint fails. Enable Pro on that machine, and it works.

I've added a note to the original hint; sorry for the lack of clarification in the original.

If you still have (or can find) a copy of Movie Player (this is QuickTime Player before it went "Pro"), you can run it in Mac OS 9 or Classic. It will have access to all of the "pro" menus, although one or two might crash it (like the controller menu).